X-ray-tube-controlling mechanism



H. A. MULVANY AND H. E. KENNEDY. X-RAY TUBE comnoumc MECHANISM.

APPUCATION FILED JAN.24. 19'8- 1,387,162. Patented Aug. 9, 1921.

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WITNESS.- l6 INVENTORS.

, I Harry (1?. Muh/an/y lgerry E.Kennedy w "z W A TTORNE YS.

UNITED STATES PATENT OFFICE.

X-RAY-TUBE-CONTBOLLING MEoHAivIsi/r.

Specification of Letters Patent. Patentd A 9 1921 Application filed January 24, 1918. Serial No. 213,475.

To all whom it may concern:

Be it known that we, HARRY A. MULVANY and HARRY E. KENNEDY, citizens of the United States, residing at Berkley, in the county of Alameda and State of California, have invented new and useful [[mprov ement in x Ray-Tube-Controlling Mechanism,-of which the following is a specification.

This invention relates toa method and means for controlling the current flow through X-ray tubes.

One of the objects of the present invention is to provide means for maintaining a uni-directional, high potential current flow through a Rontgen or X-Ray tube without the insertion of any rectifying device in either the primary or secondary of the transformer. Another object ofthe invention is to provide means for varying the resistance of the tube or what may be termed hardening or softening the same. Another object of the invention is to provide means for deflecting the cathode stream to prevent puncturing of the target. Further objects will hereinafter appear.

The invention consists of the parts and the construction and combination of parts as hereinafter more fully described and claimed, having reference to the accompa nying drawings, in which Figure 1 is a diagrammatic View of an X-ray tube, showing the application of the invention. I

Fig. 2 is a diagrammatic view similar to Fig. 1, showing the application of the magnets whereby the resistance of the tube may be varied.

Fig. 3 is a diagrammatic view of a'sine wave. i

Fig. 4 shows a modified form of magnet coil which may be used in preference to the magnets 11 and 12.

l/Vhile' investigating the effect of an electromagnet placed in close proximity to an X-ray tube, it was discovered that a rectifying action could be obtained. The magnetic field established was excited by a current in synchronism with that applied to the tube and it was observed, under certain conditions, that the brushes of the synchronous commutator'could be shifted as results strength of the magnetic field to someicritical value. We found that the best results could be obtained, as far as rectificationwas concerned, when the magnet was confined to the anode or the positive electrode.

in this manner with perfect rectification and have also doubled the current by energizing the magnetic field when the field was located behind the anode. This same field could be moved'toward the cathode, and" when thus moved to the approximate center of the tube, it would raise, the apparent pressure and entirely prevent current from The apparatus presently employed for the purpose of the X-ray tu e is illustrated particularly in Fig. 1, in Which A indicates a standard form of X-raytube, 2 the cathode electrode, 3 the anode electrode, and 4 the target; the terminals of the electrodes bemg connected by wires 5 and 6 with the secondary 7 of a high tension transformer, the primary of which is connected through wires 8 and 9' with a source of A. C. supply, a variable resistance 10 being preferably interposed in the circuit to vary the current flow through the transformer. Suitably supported adjacent to the anode electrode 3 is a pair of magnets 11 and 12 which are series connected through wires 13 and 14 with a source of direct current supply as the battery 15 here shown, a variable resistance 16 being also interposed in this circuit to vary the current fiow through the magnets 11 and 12. The magnets are preferably supported upon an adjustable bracket or like means indicated at 17 to permit their position to be changed with relation to the target 4, as will hereinafter be described.

ermittin'g rectification within The magnets 11 and 12, shown in the diagrammatic view, were a pair of old field poles of a D. C. motor. The flux which acted upon the tube was only leakage flux between the north and south pole. The magnets were energized by a constant direct current source, and we obtained good when passin 50 mille-amperes through at 70 K. by energizing the above magnets on 220 volts D. C. We

. about the 'target electrode-wouldthen be have explored the tube between the elec-- trodes and have found that the efi'ect of a field in any other place but about the anode is to harden or increase the resistance of the tube. The above is also true when the field is placed about the cathode. We at tempted to find a critical .value here where.

the current through the tube would increase due to the magnetic field. We energized the field from zero current to the maximum current; that is, all that could be forced through the magnets at 220 volts, about 5 amperes. .The efiect was to decrease the current through the tube until the same ceased to flow.

In the experiments conducted, the current through the tube was obtained from a 10 K. W. high voltage transformer shown with a maximum voltage of 100,000 operated on 50 to 120 cycles. The higher frequency has the efiect of steadying the discharge through the tube and increasing the penetration of the X-rays. The magnetic rectification seems to work as well, if not better, at 120 cycles than on cycles.

We, of course, cannot fully explain the entire phenomenon involved and feel somewhat reluctant in offering any explanation. However the most plausible-explanation presenting itself at this time is as follows: Referring to the diagram, when the cathode rays impinge on the anode target they not only propagate X-rays but negatively charged particles or electrons which move at a comparativel slow speed which can be easily deflected by a magnetic field. Now with an alternating current on the tube the electrode becomes alternately positive and negative during each cycle, thus establishing about the anode a preponderance of electrons.

With a magnetic field about the anode these electrons are confined to the neighborhood of the target which will encourage the discharge to flow when the target electrode is positive. V

Let us for a moment consider what would happen if no magnetic field was present. During the reverse half cycle the target electrode becomes negative and the aluminum electrode becomes positive. The electrons repelled toward the aluminum or now positive electrode and attracted by the same, thus permittin a discharge in the opposite direction or .w at might be termed inverse current flow. In other words, it seems that the magnetic field is able to overcome the effect of the electrostatic field set up by the charge about the electrodes and hold .the electrons about the target electrode. This. phenomenon also seems to be substantiated by the fact that when the tube is rectifying without the assistance of the'magnets and the magnetic field is energized the current through the tube can be increased, this being due,

decay nes'mea seemingly, to the fact that the electrons are concentrated or collected about the anode.

As previously stated in the specification,-

it has been found that the tube will continue rectifying even after the magnetic field has been removed. We at first thought that this self-rectifying condition would only last for a few moments, but it has lately been found that a tube continues to rectify and has, at the present time, been running several days without requiring the use of the magnets 11' phenomenon of a tube, once the magnetic.

field has been removed, may be attributed to the residual magnetism establishedjn the anode electrode, this being evidently due to the fact that it is usually constructed of iron. However, we do not wish to limit ourselves to any fixed theory or explanation as no authority on the subject has been located. We only know that a tube will rectify when the anode is subjected to a magnetic field and that rectifying action continues after the field has been removed.

. Another important feature of the invention is the provision of means for varying the resistance 'of a tube. This is accomplished by providing two magnets 17' and 18 positioned approximately centrally of the tube. These magnets are connected in series through wires 19 and 20 with a source of current supply, as the battery 21, and the flow through the magnets is interrupted by a synchronous commutator generally indicated at 22. The commutator can be set so as to harden the tube. during the period that inverse current would occur.

The above arrangement allows a very heavy current to be handled. The magnetsv located about the center of the tube have no ironin their-construction so that the rate of of the flux in these magnets will follow closely with the commutator current. The magnets are primarily" employed for the purpose of hardening or varying the resistance of the tube here shown or any other standard tube, first, by varying the current flow through the magnets by means of a variable resistance shown at 23, and, secondly, by changing the position of the synchronous commutator, as shown in the diagrammatic view of the sine wave illustrated in Fig. 3.

By referring to Fig. 3 is can be seen that the lower half of the wave is eliminated as the upper half only is selected, this being accomplished mechanically by the synchronously rotating commutator which energizes the ma et coils 17' and 18 atthe proper time. y this mechanical selector it also becomes possible to select any part of the upper half of the wave, this being. accom-- plished by increasing or decreasing the length of the segments, as shown by the dotted lines at 24, and by mounting the brush 25 in such a manner that it may be adjusted through an arc of approximately 180. For instance, the employment of the segment illustrated by the dotted lines would select the part of the upper half of the Wave shown by the dotted lines 26, while the lower segment shown in full lines would select the whole of the wave shown by the dotted lines at 27. It, therefore, becomes possible to select any portion of the upper half of the sine wave, thereby varying the current flow through the magnets 17 and 18 and either increasing or decreasing the hardnessor resistance of the tube.

Another important feature of the present invention is the adjustable mounting of the magnets 11 and 12. A slight change in the position of these magnets causes a deflection of the cathode stream impinging on the target, thereby preventing puncturing of the same or a readjusting of the target proper. That is, a constant impinging of the cathode rays at one point. on the target will soon perforate it, but this is entirely eliminated in the present instance as movement of the magnets 11 and 12 permits the cathode stream to be deflected so that any part of the target may be selected for impingement.

From the foregoing scheme of operation a very effective means is obtained for producing a uni-directional current flow through an X-ray tube. Means are also available for deflecting the cathode stream with relation to the target; and means have also been provided for adjusting the current flow to any desired value. The so-called crankiness of an X-ray tube can be compensated for as it. is. possible toregulate current and voltage values so that'any result maybe duplicated, this being of eat importance where steroscopic and scientific pictures are desired.

The arrangement shown and the mechanism employed are absolutely noiseless and safe, no revolving parts being necessary in the X-ray operating room.

While Figs. 1 and 2 show twomagnets 11 and 12, we wish -it-understood that a coil 31, such as shown in Fig.4, may be employed. This coil has in fact developed into what may be termed the preferred form as it not only permits the formation of a more uniform field of electromagnetic flux, but it is also cheaper to manufacture-and more simple to adjust as a pivotal mounting for the coil, such as'shown at 32, permits it to assume any angular position desired.

Having thus described our invention, what we claim and desire to secure by Letters Patent is- 1. A method of rendering Rontgen tubes self-rectifying which, consists in placing the electrodes of the tube in a field of magnetic- 2. A method of rendering Rtintgen tubes self-rectifying which'consists in placing the anode electrode of the tube in a field of magnetic flux.

- 3. A method for rendering Rontgen tubes self-rectifying which consists in magnetizing the anode electrode.

4. A method for rendering 'Riintgen tubes self-rectifying which consists in placing a magnet coil adjacent to the'anode electrode of means for varying the resistance of thetube, said means comprising. a magnet coil positioned adjacent to the electrodes, means for passing a current through the magnet,

and means operating in synchronism with the alternating current supplied to said tube for interrupting the current flow through the magnet coil.

7. The combination with the electrodes of an X-ray tube, means for connecting the electrodes with a high tension transformer and a. source of alternating current supply, of means for varying the resistance of the tube, said means comprising a magnet coil I positioned adjacent to the cathode electrode, means for passing a current through the magnet, means operating in synchronism .with the alternating current'supplied to said tube for interrupting the current flow through the magnet coil, and 'means for varying the current flow.

8. The combination with the electrodes of an X-ray tube,.means for connecting the electrodes with a high tension transformer,-

and a source of alternating current supply,

of a magnet coil positioned over the anodeelectrode, means for passing a current through the magnet coil, means for varying the current flow therethrough, said means comprising a variable resistance interposed between a direct current source of supply and the magnet coil.

9. The combination with'the anode elec? trode of an X-ray tube, of a magnet coil positioned adjacent to the anode, means for passing a current through said magnet to IQO render the tube self-rectifying, and means for changing the position of said magnet to permit deflection of the cathode stream With relation to the target carried by the anode.

10. The combination with the electrodes of an X-ray tube, means for connecting the electrodes With a high tension transformer and the source of alternating current supply, of means for varying the resistance of the tube, said means comprising a magnet coil adjacent to the cathode electrode, means for passing a current through the magnet, means operating in synchronism with the alternating current supply to said tube for interrupting the current flow through the magnet coil during each alternate half period of the current supply to the tube, and means for varying the current flow.

11. The combination with an X-ray tube of means for varying the resistance of the tube, said means comprising a pair of oppositely disposed magnet coils positioned about the electrodes, a source of supply of electric current and connections for placing said magnets in series, and an interrupter placed in the circuit formed by the magnets adapted to interrupt the flow of current through said coils at regular and predetermined intervals.

In testimony whereof We have hereunto set our hands in the presence of tWo subscribing Witnesses.

HARRY A. MULVANY. HARRY E. KENNEDY. Witnesses:

JOHN H. HERRING, W. W. HEALE-Y. 

